README for the MASSES image data for the pointing toward Per-emb-18 and Per-emb-21.

For each tracer, four images are delivered. Images are made using two different Briggs robust parameters of -1 and 1 (robust-1 and robust1).
The robust-1 is higher resolution while robust1 has less noise.
For each robust weighting, one delivered image is not corrected for the primary beam, while the other is corrected for the primary beam (labeled with 'pbcor').
Images not corrected for the primary beam are typically used for mapping structure, while those corrected for primary beam are typically used for measuring accurate fluxes.
For this source, the 1.3 mm continuum robust-1 image was not as high resolution as the robust1 image, and thus the 1.3 mm continuum robust-1 maps are not delivered.

The format for each image data cube in a MASSES dataverse is:
[targetname].[linename].robust[weighting].fits
[targetname].[linename].robust[weighting].pbcor.fits

Continuum images are delivered for 1.3 mm and 850 um.
The delivered spectral lines at 1.3 mm are 12CO21, 13CO21, C18O21, and N2DP.
The delivered spectral lines at 850 um are 12CO32, HCOP, H13COP.
Table A3 in the full data release paper indicates which lines are detected for each pointing.

For Per-emb-18 and Per-emb-21, there is a single SUB track taken with the ASIC correlator: 141127
For Per-emb-18 and Per-emb-21, there are two EXT tracks.
Track 150915 was taken with the ASIC correlator.
Track 161024 was taken with the SWARM correlator.
No 850 um data was taken in the EXT configuration.
All tracks were combined when imaging.

To import a fits image into miriad, the "fits" task should be used. "op=xyin" should be specified. We show an example for CO(2-1) below:
fits in=Per18Per21.12CO21.robust1.fits out=Per18Per21.12CO21.robust1.cube op=xyin

While casa can directly handle fits image files, to import the file into casa format, the task importfits can be used:
importfits(fitsimage="Per18Per21.12CO21.robust1.fits",imagename="Per18Per21.12CO21.robust1.cube")
